Evaluation of Layering and Input Motion Amplitude on Seismic Response of Earth Fills

This is a study of the seismic behavior of earth slopes exposed to vertical Ricker shear waves. Two-dimensional FLAC2D software based on the finite difference method was used for modeling. Layering in earth fill exists in natural situation, and the seismic response of the earth fills is mostly dependent on these different soil layers. When the situation of the weak layer changes in height of the earth fills, we expect to see different responses in seismic behavior of the system. The Mohr-Coulomb criterion is used to investigate the nonlinear soil behavior. To investigate the effects of the input wave frequency on the horizontal acceleration amplification coefficient (considered in this study as the response), four different frequencies, to investigate the effects of the input movement level on the response, four acceleration amplitudes, to investigate the effects of angle, three slopes with various angles and five layering modes are considered for the layering effects. This study presents the results of a numerical study on the seismic behavior of two-dimensional semi-sine shaped hills that were subjected to vertically propagating incident SV wave of the Ricker wavelet. The finite difference software is used to model and analyze the different sizes of the hills. Concentration is on topographic effects, so parameters such as shape factor (the ratio of the height to half width of the hill) and the type of ground took into account in this research. Another variable is the soil type that the difference being in ρ and vs. Therefore, according to the by Code 2800, three soil types have been investigated, each of which has been affected by the Ricker wave. The results show that the horizontal acceleration amplification coefficient overlay decreases with increasing movement and angle. Four different frequencies 1, 3, 5 and 10 Hz are studied in input motion Ricker wave. These different input motion frequencies are selected to evaluate the response of system to these frequencies when natural frequencies of soil layers differ. The effects of the frequency and the layering of the soil are also correlated so that if the input wave frequency is close to the natural frequency of the soil, in each layering mode, that layering mode reports the maximum value for the horizontal acceleration amplification coefficient. Generally, in the presence of a relatively weak layer (with Type III material), the response decreases. However, the high frequency does not follow this trend and offers significant responses. The highest amplification in horizontal acceleration happens in high frequency of soil layers or frequencies like them. The obtained responses are sharply dependent on input motion frequencies and also natural frequencies of soil layers. As it can be seen, when natural frequencies of soil layers and input motion frequencies are near each other, the highest responses are evaluated, which we can say that the resonance is happened. In this case, the highest horizontal acceleration in response results is evaluated. When weak layer exists in different soil layers, the de-amplification happens. The results show that the most de-amplification happens due to the weak soil layer. Also, results show that this high de-amplification happens in weak soil layer, and refers to the horizontal acceleration response.